The annual evapotranspiration varies in and around oases in the Tarim Basin. According to our calculations, the annual precipitation is about 25-100 mm, and annual evapotranspiration is about 100 mm at Khotan station. Since the potential evapotranspiration can reach above 500 mm in the oases, in some desert areas it can reach 1000 mm. The oases in the southern part of the Tarim Basin are located between 25 mm and 100 mm isohyet. Many oases in the northern part are located between 25 mm-200 mm isohyet and experienced 100 mm-200 mm isograms of annual evapotranspiration ; therefore, higher temperatures may still lead to a general increase in evapotranspiration.At present, the length of rivers in the desert changes greatly year by year due to fluctuations in the amount of discharge.For example, the annual discharge of the Keriya River (1991) is 7.0G×10^8 m^3, and 56% of that discharge (4.0×10^8 leaches m^3), is used as irrigation water for agriculture, while the remainder (3.0×10^8 m^3) in
… Moreto the ground, recharging the groundwater annually.The Keriya River basin can be divided into the following four regions by hydrological conditions :1) In the upper part, which is located in the Kunlun Mountains, the longitudinal change in the chemical composition of river water is complicated because of the conjunctions of tributary streams.2) The middle part contains an alluvial fan, on the toe of which the Keriya Oasis is located. In this region, the downstream change in the water chemistry of the river water is very complicated.3) In the lower part, evaporation has a great in fluence on the chemical and isotopic compositions. The river water is more concentrated chemically and isotopically heavier in the lower reach.4) In the lowermost part, where the Keriya River diverges into some channels, the downstream change in the water chemistry of the river is complex and the groundwater chemistry shows a great regional variety.The irrigated agriculture practiced in the Minfeng oasis has relied on water diverted from the Niya river. Less